In recent years, a liquid crystal display device has been often used as a flat panel display in various fields. However, there are still major issues such as a significant change in contrast or color tone due to a viewing angle, difficulty in power consumption reduction due to the necessity of a light source such as a backlight, and limitations on thickness reduction and weight reduction. Moreover, the liquid crystal display device still has another major issue regarding flexibility enhancement.
For these reasons, a light-emitting organic EL display device using organic EL elements has been recently expected as a display device as a substitute for the liquid crystal display device. Each of the organic EL elements is configured such that organic molecules forming an organic EL layer sandwiched between an anode and a cathode emit light by application of current to the organic EL layer. The organic EL display device using the organic EL elements is of the light-emitting type, and therefore, is excellent in terms of thickness reduction, weight reduction, and power consumption reduction. Moreover, due to a wide viewing angle, the organic EL display device has drawn great attention as a flat panel more advantageous than a liquid crystal panel.
Moreover, among the organic EL display devices, an organic EL display device using plastic substrates having more advantages than a glass substrate in terms of flexibility, impact resistance, and weight reduction has drawn much attention, and has such a potential that a new organic EL display device impossible in a display including a glass substrate is created.
Typically, when the organic EL element is driven for a certain period, light emission properties such as light emission brightness and light emission uniformity are significantly lowered as compared to an initial state. Reasons for lowering of the light emission properties include, for example, deterioration of an organic layer due to moisture from external air entering the organic EL element, and detachment of the organic layer and an electrode due to moisture.
For these reasons, the technique of providing an inorganic layer (a sealing layer) for preventing entrance of gas such as moisture has been disclosed. More specifically, e.g., an organic EL element sealed with a gas barrier film having a gas barrier layer on a film surface is disclosed (see, e.g., Patent Document 1).